Technical Field
The present invention relates to shafts for rotorcraft.
Description of Related Art
Traditional rotorcraft masts are fabricated from a steel forging, which typically comprises 4340 steel, 9310 low-alloy steel, or nitriding steel, such as nitralloy steel. In another example embodiment, a rotorcraft mast can be fabricated from a titanium forging. All interfacing features are machined on the outside surface of the mast. These can include splines for engaging with a planetary carrier in the rotorcraft's gearbox and a trunnion of the rotor hub, bearing raceways, spinner support, etc.
For example, as shown in FIG. 1, a conventional steel mast 101 for a rotorcraft (not shown) can comprise an elongated tubular structure having an external wall 103 made of steel. Mast 101 can include one or more end fittings 105 and 107 that allow mast 101 to be connected to the transmission, the rotor hub, and other components of the rotorcraft (not shown).
A major section of the mast may be exposed to the environment with minimum protection outside of the gearbox. This section may be critically loaded and may be susceptible to a variety of potentially damaging elements, such as debris blasts, sand blasts, chemical corrosion, ballistic, and handling damage. All of these damaging elements may result in dangerous cracking on the mast surface. Because conventional masts are mission critical parts with no redundant or “fail-safe” structures, the failure of a mast could very likely result in the loss of life and/or property.
Although great strides have been made in the area of rotorcraft masts, significant shortcomings remain.